The present invention relates to a method for spinning a multifilament thread from a thermoplastic material comprising the steps of extruding the melted material through a spinneret with a plurality of spinneret holes to form a filament bundle comprising a plurality of filaments, winding the filaments as thread after solidifying, and cooling the filament bundle beneath the spinneret.
The present invention also relates to polyester filament yarns and cords which contain polyester filament yarns.
A method of this type is known from EP-A-1 079 008. The movement of freshly extruded filaments is supported during the spinning procedure by a stream of air. Cooling thus takes place essentially through a stream of cooling agent flowing parallel to the thread. Good results are generally achieved with this type of cooling, especially with high drawing-off speeds.
A two-step cooling method for spinning a multifilament thread from a thermoplastic material is disclosed in JP 11061550. In the first cooling zone, the air flow is directed in such a way that it reaches the filaments from one side or circumferentially, and in a second zone compressed air is blown into the upper section of the cooling zone so that there is a downward flow of air parallel to the filaments. The purpose of this is to produce filaments with physical properties that are as uniform as possible.
The cooling behavior of thermoplastic polymers is certainly complicated and dependent upon a series of parameters. Especially during the cooling process, differences in the double refraction might be created over the filament cross-section, since the filament skin cools faster than the inside of the filament, i.e., the filament core. This cooling process also leads to differences in the crystallization behavior of the filaments. The cooling thus determines the crystallization of the polymers in the filament to a large degree, which is noticeable in the later usage of the filaments, for example in drawing. It is desirable for a series of applications that a high degree of cooling is achieved as soon as possible after the extrusion, in order to encourage rapid crystallization.
The cooling processes of the prior art do not fulfill, or incompletely fulfill, these requirements.